Video signal improving circuit

ABSTRACT

A video signal improving circuit comprises an input section which receives a video signal; a delay circuit which delays the video signal to generate a plurality of delayed video signals which have delayed times different from one another; an improving signal producing circuit which generates, as an improving signal, an improving amount for performing a transient improvement on the video signal based upon an original video signal before delay and the plurality of delayed video signals; a band-limiting filter which performs a frequency band limitation on the improving signal; a timing correcting circuit which causes timings of any one of the plurality of delayed video signals and the improving signal which has passed through the band-limiting filter to match with each other; and an adder which adds the improving signal which has passed through the band-limiting filter to the delayed video signal which has passed through the timing correcting circuit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Applications No. 2004-8646, filed on Jan. 16,2004, the entire contents of which are incorporated herein by reference.

BACKGOUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a video signal improving circuit.

2. Background Art

In order to clarify an edge of an image and display the image sharply, atransient improvement is performed on a video signal such as a luminancesignal or a color-difference signal. FIG. 14 is a diagram showing arising portion of a video signal before and after transient improvementis performed. A video signal X is a video signal before a transientimprovement and a video signal Y is a video signal after the transientimprovement. When a gradual-rising signal, such as the video signal X,is used, an edge of an image is blurred to become unclear, as shown inFIG. 15. On the other hand, when a sharp-rising signal, such as thevideo signal Y, is used, an edge of an image becomes clear, as shown inFIG. 16.

The transient improvement includes a luminance transient improvement toa luminance signal and a color-difference transient improvement to acolor-difference signal. The luminance transient improvement is calledLTI (Luminance Transient Improver), SRT (Super Real Transient), or thelike. The color-difference transient improvement is called CTI (ColorTransient Improver), color SRT (Color Super Real Transient) or the like.

In general, a frequency band of a video signal improved by the transientimprovement depends on characteristics of a transient improving circuit.For this reason, the transient improving circuit performs transientimprovement on even signals in a frequency band which does not requiretransient improvement. At this time, for example, when a jitter occursin a low frequency band which does not require transient improvement, anedge of the jitter is also made clear due to the transient improvement,which results in such a problem that the jitter becomes visible easily(refer to Japanese Paten Application Laid-Open (JP-A) No. 10-150582).

SUMMARY OF THE INVENTION

A video signal improving circuit according to an embodiment of theinvention comprises an input section which receives a video signal; adelay circuit which delays the video signal to generate a plurality ofdelayed video signals which have delayed times different from oneanother; an improving signal producing circuit which generates, as animproving signal, an improving amount for performing a transientimprovement on the video signal based upon an original video signalbefore delay and the plurality of delayed video signals; a band-limitingfilter which performs a frequency band limitation on the improvingsignal; a timing correcting circuit which causes timings of any one ofthe plurality of delayed video signals and the improving signal whichhas passed through the band-limiting filter to match with each other;and an adder which adds the improving signal which has passed throughthe band-limiting filter to the delayed video signal which has passedthrough the timing correcting circuit.

A video signal improving circuit according to another embodiment of theinvention comprises an input section which receives a video signal; adelay circuit which delays the video signal to generate a plurality ofdelayed video signals having delayed times different from one another; aband-limiting filter which performs a frequency band limitation on anoriginal video signal before delay and the plurality of delayed videosignals; an improving signal producing circuit which generates, as animproving signal, an improving amount for performing a transientimprovement on the video signal based upon the original video signal andthe plurality of delayed video signals which have passed through theband-limiting filter; a timing correcting circuit which causes timingsof any one of the plurality of delayed video signals and the improvingsignal to match with each other; and an adder which adds the improvingsignal to the delayed video signal which has passed through the timingcorrecting circuit.

A video signal improving circuit according to further embodiment of theinvention comprises an input section which receives a video signal; afirst delay circuit which delays the video signal to generate aplurality of delayed video signals having delayed times different fromone another; an improving signal producing circuit which generates, asan improving signal, an improving amount for performing a transientimprovement on the video signal based upon an original video signalbefore delay and the plurality of delayed video signals; an amplifiercircuit amplifying the improving amount; a frequency detecting circuitwhich detects a frequency of the plurality of delayed video signals toreduce a gain of the amplifier circuit in the case that the detectedfrequency belongs to a frequency band which does not require thetransient improvement; and an adder which adds the improving signalamplified by the amplifier circuit to one of the plurality of videosignals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a video signal improving circuit 100according to a first embodiment of the present invention.

FIG. 2 is a graph showing an improving amount of an improving signal toa frequency of a video signal.

FIG. 3 is a graph showing a gain characteristic of the band-limitingfilter 3.

FIG. 4 is a graph showing an improving amount of an improving signalwhich has passed through the band-limiting filter 3.

FIG. 5 is a block diagram of a video signal improving circuit 200according to a second embodiment of the present invention.

FIG. 6 is a block diagram of a video signal improving circuit 300according to a third embodiment of the present invention.

FIG. 7 is a graph showing an improving amount of an improving signaloutputted from the gain control circuit 26.

FIG. 8 is a graph showing an improving amount obtained when the gain ofthe gain control circuit 26 is reduced in both of a low frequency bandlower than the peak frequency and a high frequency band exceeding thepeak frequency.

FIG. 9 is a block diagram of a video signal improving circuit 400according to a fourth embodiment of the present invention.

FIG. 10 is a timing chart of an output signal S1 to S6 when the videosignal is a high frequency signal.

FIG. 11 is a timing chart of an output signal S1 to S6 when the videosignal is a low frequency signal.

FIG. 12 is a block diagram of a video signal improving circuit 500according to a fifth embodiment of the present invention.

FIG. 13 is a block diagram of a video signal improving circuit 600according to a sixth embodiment of the present invention.

FIG. 14 is a diagram showing a rising portion of a video signal beforeand after transient improvement is performed.

FIG. 15 is a diagram showing an image before transient improvement isperformed.

FIG. 16 is a diagram showing an image after transient improvement isperformed.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments according to the present invention will be explained belowwith reference to the drawings. The present invention is not limited tothe embodiments. Each of video signal improving circuits according tothe following embodiments modifies a gain of an improving amount of atransient improvement based upon a frequency of an input video signal.Thereby, the transient improvement is performed on a video signalrequiring improvement and an improving amount of transient improvementcan be reduced to other video signals. The video signal improvingcircuit is embedded in an analog television receiver, a digitaltelevision receiver or the like, and can be used for a video signalprocessing in the television receiver, a monitor device therein or thelike. In the drawings, same reference numerals denote same or similarelements or members.

FIG. 1 is a block diagram of a video signal improving circuit 100according to a first embodiment of the present invention. The videosignal improving circuit 100 comprises a transient improving circuit 2,a band-limiting filter (hereinafter, also called “BPF (Band PassFilter)”) 3, and a timing correcting filter 4. The transient improvingcircuit 2 includes delay lines 21 to 24, and an improving signalproducing circuit 25. As shown in FIG. 14, the transient improvingcircuit 2 improvs a video signal so as to make a slope of a rising orfalling of the video signal steeper.

The delay lines 21 to 24 are connected from an input terminal 1 inseries. The delay line 21 delays an original video signal inputted fromthe input terminal 1 to output a first delayed video signal. The delayline 22 further delays the first delayed video signal from the delayline 21 to output a second delayed video signal. The delay line 23further delays the second delayed video signal from the delay line 22 tooutput a third delayed video signal. The delay line 24 further delaysthe third delayed video signal from the delay line 23 to output a fourthdelayed video signal. In order to perform transient improvement easily,it is preferable that the delay lines 21 to 24 delay the video signalsby the same delay amount, respectively. The video signal is constitutedof, for example, a color-difference signal and a luminance signal, or,RGB signals.

A node between the input terminal 1 and the delay line 21 is defined asN1, a node between the delay line 21 and the delay line 22 is defined asN2, a node between the delay line 22 and the delay line 23 is defined asN3, a node between the delay line 23 and the delay line 24 is defined asN4, and a node between the delay line 24 and the improving signalproducing circuit 25 is defined as N5. The improving signal producingcircuit 25 is connected to the node N1 to N5, respectively. Thereby, theimproving signal producing circuit 25 can be inputted with the originalvideo signal, and the first to fourth delayed video signals. Theimproving signal producing circuit 25 performs arithmetic operation onthese signals using the original video signal and the first to fourthdelayed video signals to generate an improving signal indicating animproving amount based upon a slope of a rising or falling of the videosignal.

In general, a frequency of a video signal to be subjected to transientimprovement is determined according to a difference of a delay amount.In detail, when improvement is performed on a video signal with a lowfrequency, the improving signal producing circuit 25 generates animproving signal by using a plurality of video signals forming a largedifference(s) in delay amount among them. In this case, for example, theimproving signal producing circuit 25 uses the original video signal(N1), the second delayed video signal (N3), and the fourth delayed videosignal (N5) to calculate a difference between the original video signaland the second delayed video signal and a difference between the seconddelayed video signal and the fourth delayed video signal. Further, theimproving signal producing circuit 25 generates an improving signal byperforming such an operation as differentiating these differences.

On the other hand, when improvement is performed on a video signal witha high frequency, the improving signal producing circuit 25 generates animproving signal using a plurality of video signals forming a smalldifference(s) in delay amount. The improving signal producing circuit 25uses the first delayed video signal (N2), the second delayed videosignal (N3), and the third delayed video signal (N4) to calculate adifference between the first delayed video signal and the second delayedvideo signal and a difference between the second delayed video signaland the third delayed video signal. Further, the improving signalproducing circuit 25 obtains an improving signal by performing such aprocessing as differentiating these differences.

FIG. 2 is a graph showing an improving amount of an improving signal toa frequency of a video signal. A peak frequency is a frequency of avideo signal to be subjected to transient improvement. As shown in FIG.2, improving amount occurs even in frequencies other than the peakfrequency. That is, when a video signal is subjected to a transientimprovement by using an improving signal outputted from the improvingsignal producing circuit 25, video signals with frequencies other thanthe peak frequency are also subjected to a transient improvement.

Therefore, a band-limiting filter 3 connected to the improving signalproducing circuit 25 is inputted with the improving signal from theimproving signal producing circuit 25 to convert a gain of the improvingsignal dependent on a frequency. A gain characteristic of theband-limiting filter 3 is shown in FIG. 3. In this embodiment, theband-limiting filter 3 is a high pass filter. Therefore, the improvingsignal is limited regarding a low frequency band lower than the peakfrequency.

FIG. 4 is a graph showing an improving amount of an improving signalwhich has passed through the band-limiting filter 3. A broken line Sshows an improving signal before it passes through the band-limitingfilter 3, and a solid line T shows an improving signal after it passesthrough the band-limiting filter 3. Since the band-limiting filter 3 isthe high pass filter, the improving amount in the low frequency band isreduced in this manner.

The timing correcting filter 4 is connected between the node N3 and anadder 5. The timing correcting filter 4 is inputted with the seconddelayed video signal to output the video signal to the adder 5. At thistime, the timing correcting filter 4 delays the second delayed videosignal. This delay is performed for synchronizing the second delayedvideo signal with the improving signal which has passed through theband-limiting filter 3, because the improving signal is delayed bypassing of the improving signal through the band-limiting filter 3. Thetiming correcting filter 4 may be constituted of, for example, a delayline(s).

The adder 5 is connected to the band-limiting filter 3 and the timingcorrecting filter 4, respectively, and is inputted with the improvingsignal from the band-limiting filter 3 and with the second delayed videosignal from the timing correcting filter 4. Further, the adder 5 addsthe improving signal and the second delayed video signal to output theadded result from an output terminal 6. Thereby, a video signal improvedsuch as a video signal Y shown in FIG. 14 is outputted from the outputterminal 6.

A reason for inputting the second delayed video signal into the timingcorrecting circuit 4 will be explained below. As described above, when avideo signal is a signal with a low frequency, the improving signalproducing circuit 25 generates an improving signal by using the originalvideo signal, the second delayed video signal, and the fourth delayedvideo signal. When a video signal is a signal with a high frequency, theimproving signal producing circuit 25 generates an improving signal byusing the first delayed video signal, the second delayed video signal,and the third delayed video signal. In either case, the second delayedvideo signal is an intermediate signal among these delayed video signalswhich has an intermediate value between the original video signal and adelayed video signal delayed in the maximum. That is, the both of thecases use a signal delayed from the second delayed video signal by afixed time and a signal advanced from the second delayed video signal bythe same fixed time. As shown in FIG. 14, therefore, it is necessary touse the second delayed video signal in order to improve a slope of arising or a falling of a video signal about a center thereof in an arrowdirection.

According to this embodiment, as shown in FIG. 4, an improving amount tovideo signals belonging to a frequency band which does not requiretransient improvement can be reduced. Thereby, for example, even when ajitter occurs in a video signal belonging to a low frequency band, thejitter is not enhanced on a screen.

In this embodiment, though the high pass filter is used as theband-limiting filter 3, a band pass filter or a low pass filter may beused as the band-limiting filter 3. When the low pass filter is used asthe band-limiting filter 3, an improving amount to a video signalbelonging to a high frequency band exceeding a peak frequency thereofcan be reduced. When the band pass filter is used as the band-limitingfilter 3, an improving amount to a video signal belonging to a lowerfrequency band lower than the peak frequency and belonging to a highfrequency band exceeding the peak frequency can be reduced. Thereby,even when noises or the like occur in a high frequency band, or both ofa high frequency band and a low frequency band, the video signalimproving circuit 100 according to the embodiment can improve transientof a video signal with an intended frequency to display an image sharplywithout enhancing the noises.

(Second Embodiment)

FIG. 5 is a block diagram of a video signal improving circuit 200according to a second embodiment of the present invention. The videosignal improving circuit 200 is different from the first embodiment inthat the former is provided with band-limiting filters 31 to 35 insteadof the band-limiting filter 3. The band-limiting filters 31 to 35 areprovided inside a transient improving circuit 210, and the transientimproving circuit 210 is different from the transient improving circuit2 shown in FIG. 1 in this point.

The band-limiting filters 31 to 35 are connected between the node N1 andthe improving signal producing circuit 25, between the node N2 and theimproving signal producing circuit 25, between the node N3 and theimproving signal producing circuit 25, between the node N4 and theimproving signal producing circuit 25, and between the node N5 and theimproving signal producing circuit 25, respectively. The otherconstituent elements of the second embodiment may be similar to those ofthe first embodiment. Each of the band-limiting filters 31 to 35 may beeither of a high pass filter, a band pass filter, and a low pass filterlike the band-limiting filter 3.

In this embodiment, the band-limiting filters 31 to 35 performband-limitation on the original video signal and the first to fourthdelayed video signals before producing an improving signal. Thereby,this embodiment can achieve an advantage or merit similar to the firstembodiment.

(Third Embodiment)

FIG. 6 is a block diagram of a video signal improving circuit 300according to a third embodiment of the present invention. The videosignal improving circuit 300 is different from the video signalimproving circuit 100 of the first embodiment in that the former isprovided with a gain control circuit 26 and a frequency detectingcircuit 50. The gain control circuit 26 is provided inside a transientimproving circuit 310, and the transient improving circuit 310 isdifferent from the transient improving circuit 2 shown in FIG. 1 in thispoint.

The gain control circuit 26 is connected between the improving signalproducing circuit 25 and the adder 5. The frequency detecting circuit 50is connected between the node N3 and the gain control circuit 26. A gain(an improving amount) of the gain control circuit 26 is fixed orcontrolled by I²CBUS or the like. When control is performed by I²CBUS,image evaluation is performed and a gain is set based upon theevaluation result. The gain of the gain control circuit 26 can bemodified based upon a frequency detected by the frequency detectingcircuit 50. For example, the frequency detecting circuit 50 detects afrequency of the second delayed video signal, so that, when the detectedfrequency is lower than a preset threshold frequency, the gain of thegain control circuit 26 is reduced.

FIG. 7 is a graph showing an improving amount of an improving signaloutputted from the gain control circuit 26. A broken line S indicates animproving amount obtained when the frequency detecting circuit 50 is notprovided, and a solid line T and U indicates an improving amountobtained when the gain of the gain control circuit 26 is reduced. Thefrequency detecting circuit 50 may gradually reduce the gain of the gaincontrol circuit 26 according to lowering of the frequency of the seconddelayed video signal, such as the solid line T. The frequency detectingcircuit 50 may reduce the gain of the gain control circuit 26 down toalmost zero when the frequency of the second delayed video signal islower than the threshold, such as the solid line U. FIG. 7 shows thegain of the gain control circuit 26 in a low frequency band lower thanthe peak frequency, but such a constitution may be employed that thegain of the gain control circuit 26 in a high frequency band exceedingthe peak frequency is reduced.

FIG. 8 is a graph showing an improving amount obtained when the gain ofthe gain control circuit 26 is reduced in both of a low frequency bandlower than the peak frequency and a high frequency band exceeding thepeak frequency. As shown with a solid line V in FIG. 8, the frequencydetecting circuit 50 can reduce the gain of the gain control circuit 26down to almost zero when the frequency of the second delayed videosignal becomes lower than a first threshold and when the frequency ofthe second delayed video signal becomes higher than a second threshold.

This embodiment can achieve an advantage similar to that of the firstembodiment. Further, since the video signal improving circuit 300 ofthis embodiment can reduce the gain of the gain control circuit 26 toalmost zero on reaching the first threshold and the second threshold,jitters or noises present in a frequency band lower than the firstthreshold or a frequency band higher than the second threshold can becompletely prevented from being enhanced.

Incidentally, the gain control circuit 26 may be constituted as acircuit for controlling an improving amount inside the improving signalproducing circuit 25. In this case, the circuit may be used instead ofthe gain control circuit 26.

(Fourth Embodiment)

FIG. 9 is a block diagram of a video signal improving circuit 400according to a fourth embodiment of the present invention. FIG. 10 is atiming chart of signals S1 to S6 obtained when a video signal has arelatively high frequency. FIG. 11 is a timing chart of signals S1 to S6obtained when a video signal has a relatively low frequency.

The video signal improving circuit 400 is different from the videosignal improving circuit 300 according to the third embodiment in thatthe former is provided with delay lines 420, 430, and 440, a comparingcircuit 450, a double side-band rectifier 460, and a level detector 470.However, the video signal improving circuit 400 is similar to the videosignal improving circuit 300 according to the third embodiment in thatthe former detects the frequency of a video signal, thereby controllingthe gain of the gain control circuit 26. The frequency detecting circuit51 includes therein the delay line 440, the comparing circuit 450, thedouble side-band rectifier 460, and the level detector 470.

The delay lines 420 and 430 are provided for adjusting a delay time in asignal line producing an improving signal and a delay time in signalline for detecting a frequency of a video signal. The delay line 440 isconnected between nodes N6 and N7 to delay the video signal. A videosignal at the node N6 is represented as S1 and a video signal at thenode N7 is represented as S2. As shown in FIG. 10, the signal S2 isdelayed from the signal S1 by an amount corresponding to passing of thesignal S2 through the delay line 440.

Two inputs of the comparing circuit 450 are connected to the nodes N6and N7 which are inputted with the signals S1 and S2. The comparingcircuit 450 calculates a difference between the signals S1 and S2. Indetail, the comparing circuit 450 calculates (S1-S2) to output anon-inverted signal S3 and an inverted signal S4. The waveforms of thesignals S3 and S4 are shown in FIG. 10.

The double side-band rectifier 460 connected to outputs of the comparingcircuit 450 to be inputted with the signals S3 and 54. The doubleside-band rectifier 460 detects the maximum value in the signals S3 and54 to generate a signal S5. The waveform of the signal S5 is shown inFIG. 10.

The level detector 470 is connected between the double side-bandrectifier 460 and the gain control circuit 26 to be inputted with thesignal S5. The level detector 470 stores therein a predetermineddetection level L in advance to compare the signal S5 and the detectionlevel L with each other. When the signal S5 exceeds the detection levelL, the level detector 470 outputs H (high), and when the signal S5 islower than the detection level L, the level detector 470 outputs L(low). At this time, the waveform of an output signal S6 of the leveldetector 470 is shown in FIG. 10.

As shown in FIG. 11, when the frequency of the video signal is low, thewavelengths of the signals S1 and S2 become long. The peak of the signalS1 corresponds to an ascending slope portion of the signal S2, and thepeak of the signal S2 corresponds to a descending slope portion of thesignal S1, respectively. Therefore, the peaks of the signals S1 and S2are cancelled by taking a difference between the signals S1 and S2, asshown with the signals S3 and S4. Accordingly, the amplitude value ismade small as compared with the case that the video signal has a highfrequency. As a result, when the video signal has a low frequency, thesignal S5 does not exceed the detection level L and the signal S6maintains L (low).

Thus, the video signal improving circuit 400 of this embodiment candetect a frequency of a video signal. For example, when the signal S5 islower than the detection level L, the gain of the gain control circuit26 is made zero and when the signal S5 exceeds the detection level L,the gain of the gain control circuit 26 is increased. Thereby, thisembodiment can provide a characteristic as such shown by a curve U inFIG. 7. On the contrary, such a constitution may be employed that, whenthe signal S5 exceeds the detection level L, the gain of the gaincontrol circuit 26 is made zero, and when the signal S5 is lower thanthe detection level L, the gain of the gain control circuit 26 isincreased. With such a constitution, the video signal improving circuit400 of this embodiment can cut a video signal belonging to a frequencyband higher than the peak frequency.

Further, the frequency may be determined depending on periods T1 and T3where a signal S6 shown in FIG. 10 is H (high), or a period T2 betweenthe periods T1 and T3 where the signal S6 is L (low). In this case,since the frequency of a video signal can be detected in an analogmanner, the video signal improving circuit 400 of this embodiment canprovide a characteristic as such shown by a curve T in FIG. 7.

By changing the delay amount in the delay line 440 or the detectionlevel L in the level detector 470, the frequency (the threshold in FIG.7) which reduces the gain of the gain control circuit 26 can be changed.

(Fifth Embodiment)

FIG. 12 is a block diagram of a video signal improving circuit 500according to a fifth embodiment of the present invention. Thisembodiment is different from the video signal improving circuit 400 ofthe fourth embodiment in that the former further comprises a delay line441, a comparing circuit 451, a double side-band rectifier 461, and alevel detector 471 inside a frequency detecting circuit shown by abroken line. The frequency detecting circuit 51 further includes thereinthe delay line 441, the comparing circuit 451, the double side-bandrectifier 461, and the level detector 471. For example, the delay line441, the comparing circuit 451, the double side-band rectifier 461, andthe level detector 471 are used for lowering a video signal belonging toa high frequency band, while the delay line 440, the comparing circuit450, the double side-band rectifier 460, and the level detector 470 areused for lowering a video signal belonging to a low frequency band.

For this end, delay amounts in the delay lines 440 and 441 are madedifferent from each other, or the detection levels L in the leveldetectors 470 and 471 are made different from each other. Thereby, anoutput signal S6 of the level detector 470 and an output signal S7 ofthe level detector 471 become H (high) at their frequencies differentfrom each other. The signal S6 and an inverted signal of the signal S7are inputted into an AND gate AND an output signal S8 of the AND gateAND is supplied to the gain control circuit 26.

This embodiment can provide a characteristic such as shown by a curve Vin FIG. 8 by setting the delay line 440, 441 or the detection level Lproperly. For example, the delay line 440, 441, or the detection level Lis set such that, when the frequency of a video signal is lower than thefirst threshold, both the signals S6 and S7 are made L (low). At thistime, since the signal S8 is L (low), the gain of the gain controlcircuit 26 is decreased. The delay line 440, 441, or the detection levelL is set such that, when the frequency of a video signal is higher thanthe first threshold and lower than the second threshold, the signal S6is made H (high) and the signal S7 is made L (low). At this time, sincethe signal S8 is H (high), the gain of the gain control circuit 26 isincreased. Further, the delay line 440, 441, or the detection level L isset such that, when the frequency of a video signal is higher than thesecond threshold, both the signals S6 and S7 is made H (high). At thistime, since the signal S8 is L (low), the gain of the gain controlcircuit 26 is decreased. Thus, this embodiment can provide acharacteristic such as shown by a curve V in FIG. 8.

(Sixth Embodiment)

FIG. 13 a block diagram of a video signal improving circuit 600according to a sixth embodiment of the present invention. The videosignal improving circuit 600 is different from the video signalimproving circuit 500 of the fifth embodiment that the former is notprovided with the delay line 441, the comparing circuit 451, and thedouble side-band rectifier 461 but with the level detector 471. Thefrequency detecting circuit 51 includes therein the level detector 471,but does not include the delay line 441, the comparing circuit 451, andthe double side-band rectifier 461.

Since the video signal improving circuit 600 does not have the delayline 441, the signals S6 and S7 can not be controlled by the delayamount of a video signal based upon the frequency of the video signal.However, since the video signal improving circuit 600 is provided withthe level detectors 470 and 471, the signals S6 and S7 can be controlledby making the detection levels L in these level detectors different fromeach other based upon the frequency of the video signal.

This embodiment has an advantage or merit similar to that in the fifthembodiment. Further, this embodiment can be reduced in circuit scale ascompared with the fifth embodiment.

1. A video signal improving circuit comprising: an input section whichreceives a video signal; a delay circuit which delays the video signalto generate a plurality of delayed video signals which have delayedtimes different from one another; an improving signal producing circuitwhich generates, as an improving signal, an improving amount forperforming a transient improvement on the video signal based upon anoriginal video signal before delay and the plurality of delayed videosignals; a band-limiting filter which performs a frequency bandlimitation on the improving signal; a timing correcting circuit whichcauses timings of any one of the plurality of delayed video signals andthe improving signal which has passed through the band-limiting filterto match with each other; and an adder which adds the improving signalwhich has passed through the band-limiting filter to the delayed videosignal which has passed through the timing correcting circuit.
 2. Thevideo signal improving circuit according to claim 1, wherein the timingcorrecting circuit delays an inputted delayed video signal from amongthe plurality of delayed video signals.
 3. The video signal improvingcircuit according to claim 2, wherein the timing correcting circuitreceives a delayed video signal having a delay amount corresponding toan intermediate value between the original video signal and a delayedvideo signal which has been delayed the most from among the plurality ofdelayed video signals.
 4. The video signal improving circuit accordingto claim 1, wherein the timing correcting circuit receives a delayedvideo signal having a delay amount corresponding to an intermediatevalue between the original video signal and a delayed video signal whichhas been delayed the most from among the plurality of delayed videosignals.